Chemistry Reference
In-Depth Information
TMS
TMS
O
O
HO
OH
TMSCCH, BuLi,
CeCl
3
,THF-78 C
50%
HO
OH
O
O
50
TMS
TMS
1) TsOH, PhCH
3
,
2) KOH, MeOH, rt
30%
TMS
TMS
TMS
TMS
1) CpCo(C
2
H
4
)
2
BTMSA, DME, rt
2) Cp
2
FePF
6
2%
TMS
TMS
TMS
TMS
52
51
Scheme 14 Synthesis of quadrannulene 52 [
66
]
2.5 Polymeric and Graphitic [N]Phenylenes
Currently, ladder polymers and 2D or 3D graphitic materials containing phenylenes
have mostly been an area of theoretical interest due to synthetic challenges. Inspired
by the successful synthesis of the [N]heliphenes up to
N
9[
30
,
31
], calculations
on the properties of even longer linear, angular, and helical phenylenes, of
N
¼
14,
19, and 24, were reported in 2003 [
67
]. Notably, in each case the authors found that
bond lengths and NICS value converge on the centermost rings (Fig.
10
), the zigzag
and helical topologies taking on increased bond alternation, while all bonds of the
six-membered rings are nearly equal in the linear topology.
Despite the increase in bond alternation, isotropic magnetic susceptibility
calculations indicate that the zigzag topology is the most aromatic followed closely
by the helical analogue. For zigzag and helical topologies the terminal benzenoid
ring is the most aromatic while the penultimate is the least, whereas for the linear
case aromaticity decreases from the terminus towards the center. The four-
membered rings in the linear topology are more antiaromatic than their zigzag
and helical counterparts.
The polyhedral carbon allotrope containing phenylene units and a molecular
formula of C
120
is known as archimedene 53 (Fig.
11
)[
69
-
75
]. Ab initio
calculations were performed on 53 as well as eight related bowl-shaped
hydrocarbons in 2005 by Schulman and Disch [
76
]. The resulting geometries are
very consistent with what has been shown experimentally for angular and branched
[N]phenylenes: the six-membered rings have significant bond alternation, 1.479
˚
and 1.364
˚
, and the four-membered rings are nearly square. NICS values for the
¼
